A liquid crystal display apparatus is a display that is driven at a low voltage and consumes low electric power and is widely used in a display unit of a clock, an electronic desk calculator, an electronic game, a remote controller, a price tag, and the like.
In the related art, this type of liquid crystal display apparatus is provided with a plurality of scanning electrodes (common wirings) extending in a row direction and a plurality of signal electrodes (segment wirings) extending in a column direction so as to intersect the common wirings. Pixels are formed so as to correspond to intersecting positions between the common wirings and the segment wirings. As a method of driving the liquid crystal display apparatus, a multiplexing drive method is mainly used. In the multiplexing drive method, the common wirings are sequentially selected and driven, and a drive voltage corresponding to a display image is applied to the segment wirings in synchronization with a selection period of the common wirings.
As a method of adjusting contrast in the display image, a method of controlling the drive voltage is typically used. As a higher drive voltage is applied, the contrast in the image increases. In contrast, as a lower drive voltage is applied, the contrast in the image decreases. In order to adjust the contrast in the image by making the drive voltage variable, it is necessary to add a voltage boosting circuit (power source circuit) provided with a voltage adjusting circuit to the liquid crystal drive device or to adjust the voltage applied from the outside to the liquid crystal drive device. Therefore, the size of the circuit will increase.
However, a power source voltage provided to the liquid crystal drive device, which is mounted on a device using this type of liquid crystal display apparatus, is typically low, such as about 1.5 to 5 V in order to meet low power consumption requirements. Therefore, there is a problem in which the addition of the voltage boosting circuit to the inside of the apparatus and the adjustment of the voltage applied from the outside leads to an increase in the size of the circuit, an increase in cost and an increase in the size of the chip.
In this regard, a liquid crystal drive device has been proposed which was capable of adjusting shading of an image by providing a contrast adjustment period for setting the same potential for the common wirings and the segment wirings after applying the drive voltage corresponding to a desired display image to the segment wirings for a predetermined period. That is, as a shorter contrast adjustment period is set, the contrast in the image increases. In contrast, as a longer contrast adjustment period is set, the contrast in the image decreases.
However, if the contrast is adjusted by adding the contrast adjustment period, a frame period, which includes a period in which the drive voltage is applied, and the contrast adjustment period will vary in accordance with a degree of the shading. Therefore, to resolve this problem it is necessary to add an adjustment circuit so that the frame period is held constant. However, due to the addition of the adjustment circuit, the size of the circuit will need to increase.